The present invention relates to an ink jet head for use in ink jet printers and to a method for the manufacture of such an ink jet head. The technical field of the present invention pertains particularly to an ink jet head of the type of emitting ink by a piezoelectric actuator having a structure-improved vibration plate.
In recent years, the ink jet printer has been used widely for business/home use. In order to meet recent demands for noise reduction, printing quality improvement, et cetera, several methods have been proposed for ink jet heads for use in ink jet printers. Generally, ink jet heads can be classified roughly into the following two types.
In the first type, a portion of a flowpath or a portion of an ink chamber is formed, as a pressure chamber, by a piezoelectric actuator having a piezoelectric element. Then, a pulse-like voltage is applied to the piezoelectric element, thereby causing the piezoelectric actuator to undergo deformation. As a result, the pressure chamber is so deformed that its volume is reduced. This generates in the pressure chamber a pressure pulse which forces droplets of ink to be emitted from a nozzle in communication with the pressure chamber.
In the second type, a heat generating resistor is disposed in a flowpath. A pulse-like voltage is applied to the heat generating resistor. The heat generating resistor generates heat, thereby bringing the ink in the flowpath to the boil to generate vapor bubbles. Droplets of the ink are emitted from a nozzle by the pressure of the generated vapor bubbles.
The present invention pertains to the first type. Therefore, the first type is further described in detail. Referring to FIGS. 9 and 10, there is shown an ink jet head as an example of the first type. This ink jet head is provided with a head main body 101 in which a plurality of recessed portions 102 for pressure chambers are formed. Each recessed portion 102 has a supply opening 102a for supplying ink and an emission opening 102b for emitting the ink. The recessed portions 102 of the head main body 101 are arranged such that they are spaced at specified intervals in one direction.
The head main body 101 is made up of a pressure chamber component 105 defining sidewalls of the recessed portion 102, an ink flowpath component 106 defining a bottomwall of the recessed portion 102 and formed by lamination of a plurality of thin plates, and a nozzle plate 113. Formed in the ink flowpath component 106 are an ink flowpath 107 for supply which is connected to the supply opening 102a of the recessed portion 102 and an ink flowpath 108 for emission which is connected to the emission opening 102b of the recessed portion 102. Each ink flowpath 107 is connected to an ink supply chamber 110 extending in the direction in which the recessed portions 102 are arranged. The ink supply chamber 110 is connected to an ink supply aperture 111 formed through the pressure chamber component 105 and the ink flowpath component 106 and connected to an ink tank (not shown). Formed through the nozzle plate 113 is a nozzle aperture 114 connected to the ink flowpath 108.
A piezoelectric actuator 121 is provided atop the pressure chamber component 105 of the head main body 101 in a corresponding fashion to the recessed portion 102. Each piezoelectric actuator 121 has a vibration plate 122 blocking up the recessed portion 102 of the head main body 101 to form, together with the recessed portion 102, a pressure chamber 103. This vibration plate 122 is common to all the piezoelectric actuators 121, serving also as a lower electrode common to all piezoelectric elements 123 which will be described later. Each piezoelectric actuator 121 has a piezoelectric element 123 provided at a portion of the top surface of the vibration plate 122 corresponding to the pressure chamber 103 and an upper electrode 124 provided atop the piezoelectric element 123 for the application of voltage to the piezoelectric element 123.
In the piezoelectric actuator 121, when a pulse-like voltage is applied, through the vibration plate 122 acting as a lower electrode and the upper electrode 124, to the piezoelectric element 123, the piezoelectric element 123 shrinks in a direction perpendicular to its thickness direction, whereas neither the vibration plate 122 nor the upper electrode 124 shrinks. As a result, a portion of the vibration plate 122 corresponding to the piezoelectric element 123 is deflected and deformed by the so-called bimetal effect, being formed into a convex shape toward the pressure chamber 103. This deflection/deformation generates a pressure in the inside of the pressure chamber 103. By this pressure, the ink in the pressure chamber 103 is emitted outside from the nozzle aperture 114 by way of the emission opening 102b and the ink flowpath 108.
Recently, various attempts have been made for further improvements in order to meet severe demands for size/weight reduction, drive voltage reduction, noise reduction, cost reduction, and improvement in ink emission controllability. With a view to achieving further miniaturization and high performance, there has been made the attempt that the vibration plate and the piezoelectric element are formed of thin films capable of easily being subjected to fine processing (capable of easily being down-sized and precisely processed).
However, if reduction in film thickness is tried by simply employing materials, shapes, and configurations of conventional piezoelectric actuators, this will produce problems such as the occurrence of cracking in the vibration plate, piezoelectric element, or upper electrode, film debonding, film expansion, at the time of manufacture, therefore leading to the drop in ink jet head productivity.
Additionally, also at the time when the ink jet head is in use, such simple reduction in film thickness inevitably results in the drop in mechanical strength because the thickness of each portion is thin. Therefore, cracking is likely to occur in the vibration plate which frequently undergoes deformation, thereby reducing the life of the ink jet head. Therefore, there have been demands for the realization of an ink jet head which is miniaturized and achieves high performance in ink emission amount controllability and, in addition, which provides longer life because of excellent component strength and is easy to manufacture.
Bearing in mind the above points, the present invention was made. Accordingly, an object of the present invention is to provide an ink jet head of the type that ink in a pressure chamber is emitted by a piezoelectric actuator which is miniaturized and improved in productivity and reliability as high as possible by providing a devised structure for a vibration plate of the piezoelectric actuator.
In order to achieve the above object, in the present invention the vibration plate is made up of at least two layers having different Young""s moduli. Alternatively, the vibration plate is made up of at least one compressive residual stress layer having a compressive residual stress and at least one tensile residual stress layer having a tensile residual stress.
The present invention provides an ink jet head comprising:
a head main body with a recessed portion for a pressure chamber formed therein, the recessed portion having a supply opening for supplying ink and an emission opening for emitting the ink; and
a piezoelectric actuator including a vibration plate blocking up the recessed portion of the head main body so as to form, together with the recessed portion, the pressure chamber, a piezoelectric element provided on a portion of a side of the vibration plate opposite the head main body and corresponding to the pressure chamber, and an electrode, provided at a side of the piezoelectric element opposite the vibration plate, for the application of voltage to the piezoelectric element, wherein, when a voltage is applied, through the electrode, to the piezoelectric element, the portion of the vibration plate corresponding to the pressure chamber undergoes deformation, thereby causing ink in the pressure chamber to be emitted out of the emission opening;
wherein the vibration plate of the piezoelectric actuator is formed by laminating together at least two layers having different Young""s moduli in the thickness direction of the vibration plate.
As a result of such a structure, the vibration plate is composed of at least two different materials. Therefore, when the layers of the vibration plate are formed, they produces different internal stresses (strains), and in the entire vibration plate the internal stresses (strains) are cancelled. As a result, excessive stress concentration to the vibration plate, the piezoelectric electric element, et cetera can be suppressed. Accordingly, even when the vibration plate and the piezoelectric element are reduced in thickness, they are prevented from cracking at the time of their film formation and when being used, therefore achieving improvement in productivity and reliability.
It is preferable that the Young""s modulus of each of the layers of the vibration plate is set at values ranging from 50 GPa to 350 GPa. This not only provides an amount of deflection sufficient enough to cause ink to be emitted but also makes it possible to provide a sufficient increase in the generated pressure affecting the ink emission rate. Therefore, the ink jet head superior in ink emission performance will be obtained.
It is preferable that at least one of the layers of the vibration plate nearmost the head main body is made of a material having ink corrosion resistance. As a result of such arrangement, even when the vibration plate is constructed such that it is brought into direct contact with ink, neither expansion/shrinkage nor deterioration by the ink occurs, and even when used for a long time, cracking or the like is unlikely to occur.
It is preferable that the ink corrosion resistant material is made of one of simple substances of copper, nickel, chromium, titanium, molybdenum, stainless steel, and tungsten, one of oxides, nitrides, and carbides of the simple substances, or an alloy selected from a group of alloys containing the simple substances, respectively. As a result of such arrangement, the vibration plate which is thin but strong can be obtained easily and dissolution/corrosion caused by ink can be prevented without fail. Further, it is possible to sufficiently increase the pressure that is generated in the pressure chamber.
It is preferable that the total thickness of the vibration plate is set at values ranging from 1 xcexcm to 7 xcexcm. This is because if the total thickness of the vibration plate is below 1 xcexcm it becomes difficult to secure the strength of the vibration plate and the pressure that is generated in the pressure chamber becomes insufficient, while on the other hand if the total thickness is above 7 xcexcm there occurs film debonding or cracking at the film formation time and the amount of deflection necessary for the emission of ink cannot be obtained sufficiently. Therefore, it is possible to improve the ink jet head productivity and reliability as well as the ink emission performance to a further extent.
The present invention provides another ink jet head comprising:
a head main body with a recessed portion for a pressure chamber formed therein, the recessed portion having a supply opening for supplying ink and an emission opening for emitting the ink; and
a piezoelectric actuator including a vibration plate blocking up the recessed portion of the head main body so as to form, together with the recessed portion, the pressure chamber, a piezoelectric element provided on a portion of a side of the vibration plate opposite the head main body and corresponding to the pressure chamber, and an electrode, provided at a side of the piezoelectric element opposite the vibration plate, for the application of voltage to the piezoelectric element, wherein, when a voltage is applied, through the electrode, to the piezoelectric element, the portion of the vibration plate corresponding to the pressure chamber undergoes deformation, thereby causing ink in the pressure chamber to be emitted out of the emission opening;
wherein the vibration plate of the piezoelectric actuator is formed by laminating together at least one compressive residual stress layer having a compressive residual stress and at least one tensile residual stress layer having a tensile residual stress in the thickness direction of the vibration plate.
As a result of such arrangement, in the case that the vibration plate is formed of the foregoing residual stress layers, the vibration plate will be prevented from being formed by crystal growth in one direction, thereby relaxing strain generated from in-crystal defect and opening gap and suppressing the occurrence of film debonding. As a result, the acceptable good ratio at the ink jet head manufacture time will be improved and, in addition, the ink jet head life will be increased. Accordingly, it is possible to achieve improvements in ink jet head productivity and reliability.
It is preferable that the residual stress of the compressive residual stress layer of the vibration plate is set at 300 GPa or below, and that the residual stress of the tensile residual stress layer of the vibration plate is set at 200 GPa or below. The reason is that if the residual stress of the compressive residual stress layer is greater than 300 GPa, then the compressive stress is increased to an excessive extent, resulting in the occurrence of cracking and debonding in the vibration plate. On the other hand, if the residual stress of the tensile residual stress layer is greater than 200 GPa, then the film becomes cloudy or is colored black, failing to become a normal mirror finished film and therefore being incapable of functioning as a vibration plate. Accordingly, it is possible to maintain the performance of an ink jet head at an excellent level while improving its productivity and reliability.
It is preferable that both of the residual stress layers of the vibration plate are made of the same material having ink corrosion resistance. As a result of such arrangement, even when the vibration plate is constructed such that it is brought into direct contact with ink, neither expansion/shrinkage nor deterioration by the ink occurs, and even when used for a long time, cracking or the like is unlikely to occur. Moreover, the adhesion between the residual stress layers can be increased to a maximum extent.
It is preferable that the ink corrosion resistant material is made of one of simple substances of copper, nickel, chromium, titanium, molybdenum, stainless steel, and tungsten, one of oxides, nitrides, and carbides of the simple substances, or an alloy selected from a group of alloys containing the simple substances, respectively. As a result of such arrangement, the vibration plate which is thin but strong can be obtained easily and dissolution/corrosion caused by ink can be prevented without fail. Further, it is possible to sufficiently increase the pressure that is generated in the pressure chamber.
It is preferable that the total thickness of the vibration plate is set at values ranging from 1 xcexcm to 7 xcexcm. As a result of such arrangement, it becomes possible to secure the strength of the vibration plate as well as to sufficiently increase the pressure that is generated in the pressure, and neither film debonding nor cracking occurs at the film formation time. In addition, the amount of deflection necessary for the emission of ink can be obtained sufficiently. It is therefore possible to further improve not only the ink jet head productivity/reliability but also the ink emission performance.
The present invention provides a method for the manufacture of an ink jet head in which ink in a pressure chamber is emitted by causing a vibration plate to undergo deformation by the piezoelectric effect of a piezoelectric element, the ink jet head manufacture method comprising the steps of:
forming on a substrate an electrode and the piezoelectric element in a superposed manner with the electrode disposed nearer to the substrate;
forming on the piezoelectric element the vibration plate by laminating together at least one compressive residual stress layer having a compressive residual stress and at least one tensile residual stress layer having a tensile residual stress in the thickness direction of the vibration plate by a sputter technique;
adhering together the vibration plate and a pressure chamber component defining the pressure chamber; and
after the adhering step, removing the substrate.
Since the vibration plate is formed by sputtering such as high frequency sputtering, DC sputtering, et cetera, this makes it possible to perform accurate control of the film thickness of each layer by time management. In addition, it is possible to form the residual stress layers by performing adequate control of the film stress by changing parameters, such as the substrate temperature, sputter gas pressure, sputter power, TS interval (the target/substrate distance), of various sputter conditions. At this time, none of film expansion, film debonding, and the like will occur in components such as the vibration plate and the piezoelectric element, as described above. Further, sputtering, being suitable for mass production, may be used to form not only the vibration plate but also the electrode and piezoelectric element. Therefore, it is possible to manufacture inexpensive ink jet heads at a greater yield in large quantities.
It is preferable that the residual stress of the compressive residual stress layer of the vibration plate is set at 300 GPa or below, and that the residual stress of the tensile residual stress layer of the vibration plate is set at 200 GPa or below. As a result of such arrangement, it is possible to maintain the performance of an ink jet head at an excellent level while improving its productivity and reliability, as described above.
It is preferable that the compressive and tensile residual stress layers of the vibration plate are formed by control of the pressure of a sputter gas. This makes it possible to perform control of the in-film stress state in a much easier way, and the compressive and tensile residual stress layers can be formed easily. Gas pressure control is determined by the amount of gas (for example, Ar gas) introduced and the amount of opening of an orifice of a vacuum pump. The operation is accurately controllable and has repeatability, therefore improving the ink jet head productivity to a further extent.